We wish to understand how specific genes are activated in specific cells and at specific times during development. As a model system we have chosen the developing erythroblasts from chick embryos. Hb first appears in these embryos at 35 hours of development. The first cells to make detectable quantities of Hb are themselves destined to give rise to 6 subsequent generations of erythroblasts. This system allow us to focus on what I believe are the three most interesting questions in developmental biology: (1) Why does Hb (and Hb mRNA) first appear in specific cells of the chick embryo at precisely 35 hours? What factors control this timing and what factors determine which cells begin to produce Hb? (2) What are the molecules that are responsible for causing the globin gene to adopt an "active" nucleosomal conformation (see for example, Weintraub & Groudine, 1976) in these cells and not in other cells of the developing embryo? (3) How is the information for keeping the globin gene active transmitted to progeny cells through 6 subsequent divisions? Alternatively, how might one "active" parental nucleosome give rise to two daughter nucleosomes that are also in an active conformation for transcription?